A friend in a church group recently posed an interesting question: how much dirt would it take to cover Cary, NC (our hometown) in a foot of dirt? Ignoring all of the terrible human suffering this would cause, it’s actually an interesting question. So, I decided to go about figuring it out.
The Easy Way
So… “covering in a foot of dirt” could be interpreted two different ways. We’ll start with the easy way – putting one foot of dirt everywhere, kind of like a blanket of snow.
According to Wikipedia, Cary is 55.4 square miles, or 1,544,463,360 square feet. That makes for simple math.
1,544,463,360 ft^2 * 1 ft = 1,544,463,360 ft^3
So, it would take 1.5 billion cubic feet of dirt to cover Cary. But that’s not really a very interesting answer… let’s see if we can do better.
The Hard Way
Instead of putting down a snow-like blanket of dirt, what if we wanted to turn Cary into a giant flat-topped mountain by burying everything in dirt so deep that the very highest point of town was covered in a foot of dirt and the lowest points of town were potentially covered in hundreds of feet of dirt. Instead of just needing to do a lot of sweeping, getting the town back to normal would now require a major archaeological excavation. This seems like a far more interesting way to approach the question.
So, how do we go about figuring that out? Well, first, we need to know what the highest point in town is. We’ll also need to know the average elevation of the town. The amount of dirt needed will then be given by the following formula:
(Highest Point – Average Elevation +1) * Area
According to the Town of Cary website, the highest point in town is at 520 feet above sea level, just outside of Cary Elementary School. Incidentally, they also report that the lowest point is only 235 feet above sea level, which means that we’re likely going to need a lot of dirt! But what’s the average elevation?
Unfortunately, average elevation doesn’t seem to be listed on the internet anywhere… So I needed to calculate it myself. Without going into too much detail, I used Geographic Information Systems software to process grid-based elevation data sets on Wake and Chatham Counties from NC State University. I selected out the grid cells that fell within the Cary city limits and averaged their elevation values together to get an average elevation: 383.21 feet.
Before I plugged numbers into our equation from above, I decided to check what the NC State data reported as the highest point in Cary. It was located in the same area, but this data reported it as 526.7 feet (as opposed to the 520 feet listed by the town). That’s pretty close, especially given that there are many different ways to go about determining elevation.
So, now we simply have to do the math!
(526.7 ft – 383.21 ft + 1 ft) * 1,544,463,360 ft^2 = 223,159,510,886 ft^3
That’s 223 billion cubic feet of dirt. 8.3 billion cubic yards. Over 590 million dump trucks full. In other words, a lot of dirt.
Moving that much dirt would be a completely unprecedented engineering marvel – requiring moving about 30 times as much dirt as was moved in the excavation of the Panama Canal, a 50-year long project which cost tens of thousands of lives and a cool $350 million (in 1914 dollars).
Maybe Bagger 288 could help…